Constant velocity fixed ball joints in the form of counter track joints, have an outer joint part with outer tracks, an inner joint part with inner tracks, torque transmitting balls which are received in pairs of tracks consisting of outer tracks and inner tracks, and a ball cage with cage windows in which the balls are held in a common plane and are guided on to the angle-bisecting plane when the joint is articulated. In such joints, first outer tracks, together with first inner tracks, form first pairs of tracks whose control angles open in a first axial direction, and second outer tracks, together with second inner tracks, form second pairs of tracks whose control angles open in a second axial direction. The control angles are defined as angles between the tangents at the ball contact points in the tracks when the joint is in the aligned condition. The present invention concerns counter track joints having four first outer tracks and four second outer tracks which alternate and are uniformly circumferentially distributed. In the inner joint part, there are provided four first inner tracks and four second inner tracks which alternate and are uniformly circumferentially distributed. The first outer tracks and the first inner tracks, together, form first pairs of tracks which, when the joint is in the aligned condition, widen in a first direction. The second outer tracks and the second inner tracks, together, form second pairs of tracks which, when the joint is in the aligned condition, widen in an opposite direction. A ball is held in each of the pairs of tracks. The annular cage comprises eight circumferentially distributed cage windows which each accommodate one of the balls and hold the balls, in their entirety, in a common plane by means of their centers.
Counter track joints, in general, are known from DE 100 60 119 A1 of the applicant, wherein the counter track joints are illustrated and described as having six torque transmitting balls. Rzeppa fixed joints with identical pairs of tracks with six torque transmitting balls wherein, for assembly reasons, the cage windows have different circumferential lengths, are described in U.S. Pat. No. 5,509,856 also owned by the applicant herein. From JP 2001 232 945 A, there are known Rzeppa fixed joints with identical pairs of tracks which comprise eight balls and wherein at the outer ball tracks, at the aperture end, there are provided assembly pockets for inserting balls when the joint is over-articulated.
There are certain disadvantages associated with the assembly of constant velocity joints wherein first the outer joint part, cage and inner joint part are joined in one of the ways commonly known. That is, typically, the balls are inserted by over-articulating the joint, i.e. articulating the inner joint part and cage relative to the outer joint part, thus enabling a cage window of the ball cage to project from the outer joint part and permitting a ball to be inserted into the cage window from the radial outside. When the cage windows are already largely filled with balls, the so-called method of over-articulating—because of the relative circumferential movement of the balls in the cage relative to one another—requires a circumferential cage window length which is needed during assembly only, but not under operational conditions of the joint. In other words, the maximum operating angle of articulation does not dictate the cage window length. Rather, the extended cage window length is necessary only for assembly. Such lengthening of the cage windows in the circumferential direction leads to a reduction in the web width between the cage windows in the circumferential direction, and thus to a weakening of the ball cage. Experience shows that, in operation, the cage constitutes a potentially frangible component which should be designed so as to be as strong as possible. Thus, there exists a need for an eight-ball counter track joint having improved cage strength or durability.